Pikovskaya Medium Research Articles

Phosphate-solubilizing fungi for efficient soil phosphorus management

Rhizosphere soil extracts obtained from eight cinnamon species and three pepper species cultivated organically were inoculated initially on Pikovskaya (PVK) medium. The twelve fungal isolates that solubilized the insoluble phosphates were further tested on the same medium added with both insoluble tricalcium phosphate and soluble dipotassium hydrogen phosphate to detect the expression of the trait in the presence of soluble phosphates in soil, for which all twelve qualified. The efficiencies of phosphate solubilization were investigated in two liquid media: PVK medium to represent soil phosphate pool and a rock phosphate (RP) medium, by determining the available phosphorus concentration in the liquid media at the end of the 24 h and 72 h incubation periods, respectively. The pH reduction in the medium was measured to ascertain the organic acid production by fungal isolates as a mechanism of solubilization. Three fungal isolates showing the highest efficiencies in phosphate solubilization were taxonomically identified based on the micromorphological characteristics and molecular techniques. Two isolates were identified as Penicillium oxalicum and Trichorderma virens and the other was belonging to the genus Aspergillus. A possible synergism between the three fungal species towards phosphate dissolution was detected using the broth culture procedure. Aspergillus sp. in combination with P. oxalicum dissolved both Ca3(PO4)2 and RP recording the highest significant dissolved phosphate levels of 893.43 (±56.768) mg P/L and 309.42 (±42.52) mg P/L, respectively, within 72 h post inoculation, making them prospective candidates for increased phosphate availability of soil phosphate pool and rock phosphates.

Isolation and characterization of efficient Phosphate Solubilizing <i>Bacillus</i> (PSB) from different agro-ecological zones of Tigray soil, Ethiopia

Applications of biofertilizer have great practical importance for increasing fertility of the soil and reducing environmental pollution. Screening and characterizing phosphate solubilizing Bacillus (PSB) strains from different agroecologies of Tigray soil and in vitro assessment for the adaptability under different abiotic stress would help in selecting the most efficient strain for use as biofertilizer. A total of 64 soil samples were collected from different agro-ecological zones of Tigray and checked for the presence, capability and efficiency of PSB. Out of 64 soil samples 21 of them were phosphate solubilizing. These phosphate solubilizing strains again incubate at 37˚C for 48h on pikovskaya medium to see efficacy of phosphate solubilization. Highest efficiency was recorded in MUB28, MUB47and MUB64 isolates and also tolerant to acidity and alkaline up to pH4 and pH8, respectively. And difference was recorded in saline tolerance among the strains: MUB47 is the most saline tolerance strain which tolerate saline up to 513mM of sodium chloride (NaCl) but MUB28 and MUB64 have tolerated saline up to 340mM of NaCl. The identification of efficient PSB candidate strains with salt & pH tolerant features in the soil sample could have an implication on the end-users to obtain the desired beneficial effect such as maintaining soil healthy, provision of adequate phosphorus from soil to the plant and improving crop yield of Tigray Agriculture. Based on the morphological, microscopic, biochemical and physiological characterization, it may be inferred that the diversity among these efficient PSB strains is low. Keywords : Biofertilizer, Phosphate solubilizing Bacillus, Efficiency, Diversity, Agroecology, Adaptability, Ethiopia.

The Potential Use of Plant Growth-Promoting Rhizobacteria (PGPR) as Antagonists and Biocontrol Agents in Hevea Diseases

The rhizosphere related bacterial species have a significant capability in plant growth promotion, referred to as Plant Growth Promoting Rhizobacteria (PGPR). Several substances produced by antagonistic rhizobacteria have been related to pathogen control and indirect promotion of growth in many plants. The objectives of this study were to identify effective PGPR bacteria in rubber soils of Sri Lanka, determine the potential use as antagonists and biocontrol agents to control economically important Hevea diseases in nurseries, and identify effective novel inoculant formulations. Soil samples were collected from the root rhizozphere of cover crops in Hevea fields in Rubber Research Institute of Sri Lanka (RRISL), Dartonfield. Bacteria were isolated by TSA plate method. Isolated PGPR bacteria were subjected to test the enzyme secretion ability. Pectinase, Lipase, and Amylase secretion ability of PGPR were tested in specifically developed media. Auxin production of PGPR were measured using freshly prepared Salkowsky reagent. Phosphorous solubilizing ability of PGPR was tested using Pikovskaya (PVK) medium. Antagonistic ability of PGPR was tested against the Rigidoporous microporus, Fusarrium sp. and Pythium sp. causing white root disease and Patch Canker disease in rubber respectively. Paper disc diffusion method was used to test the antagonism of selected bacteria and the percentage growth inhibition was calculated. Plasmid DNA extraction of antagonistic PGPR was done following the alkaline SDS method. Gene sequencing of selected bacteria was further carried out. Among 13 selected PGPR bacterial species, 3 bacteria were showing significant antagonism towards R. microporus. (Percentage growth inhibition by 51.2%, 46.8% and 44.3% respectively) Fusarium sp. was controlled by 7 PGPR species. Pythium sp. was controlled by 2 PGPR (Percentage growth inhibition by 41.6% and 38.7% respectively) 5 types of combinations of bacteria were tested. Among 5 types, 2 types were highly effective in control of R. microporus (Percentage growth inhibition by 79.8% and 72.6% respectively). All 5 combinations were moderately effective in control Fusarium sp. and 1 type was highly effective in control of Pythium sp. (Percentage growth inhibition by 67.8%). PGPR can be used as effective biocontrol agents in control of Hevea pathogens. The combinations of PGPR are more effective than the individual bacterial species. This will be leading to improve the productivity of Hevea plantations in Sri Lanka. Keywords: Plant Growth Promoting Rhizobacteria, Antagonism, Hevea pathogens

Bioprospecting Aspergillus section Nigri in Atlantic Forest soil and plant litter

ABSTRACT: The use of fungi as a source of enzymes has become widespread in various industrial and commercial areas, and Aspergillus section Nigri has significant potential for producing enzymes. The aim of this study was to isolate Aspergillus section Nigri from plant litter and soil from the Atlantic Forest biome and evaluate it with regards to hydrolytic enzyme production. The trials for producing the enzymes were carried out in Petri dishes, using different culture mediums adapted for microbial growth and with the respective substrates for inducing enzyme production - cellulase (carboxymethyl cellulose), protease (skimmed milk), amylase (soluble starch), pectinase (citrus pectin), and phytase (Pikovskaya medium). Forty-two fungi were isolated, 16.7% derived from the plant litter layer and 83.3% derived from soil at a depth of 0 to 5 cm and 5 to 10 cm. All of the isolated lineages presented amylase, protease, and phytase production, with 90.4% producing cellulase and no lineage producing pectinase. From the results, the significant potential for Atlantic Forest fungi as hydrolytic enzyme producers could be perceived. The enzymatic activity evaluations presented a satisfactory result when compared with the scientific literature.

Buffering capacity affects phosphorous solubilization assays in rhizobacteria

Phosphate solubilizing activity of phosphate solubilizing bacteria (PSB) is affected by buffering capacity of soils. It is well known that the buffering capacity of soils can diminish the efficiency of microbial acid production in phosphorus (P) solubilization process. Hence, in the first step of this study by using solid and liquid Sperber media containing organic or inorganic phosphate, more than 100 isolates were isolated, and finally two capable isolates (C1-1O and C16-2O) with highest potential of phosphate solubilizing activity were candidate for identification, and identified as Pseudomonas sp. C16-2O and Pseudomonas sp. C1-1O. In the next stage, their efficiency along with six more chosen PSB (including Pseudomonas putida P13, P. fluorescens Tabriz, Pantoea agglomerans P5, P. agglomerans P5-n, Azotobacter sp. SP5 and Azotobacter sp. SP16) in solubilizing phosphorus ‎from two P sources (rock phosphate: RP and tricalcium phosphate: TCP) in the buffered (100mM Tris–HCl) and un-buffered Pikovskaya's media were evaluated. According to in-vitro experiments, P. fluorescens Tabriz, P. agglomerans P5-n, Azotobacter sp. SP16 and Pseudomonas sp. C16-2O showed the highest solubilization overall, ranged from 258 to 252.7mgL−1. Our results revealed that thoroughly P solubility in buffered condition decreased by 56.2%. Also in the buffered condition, P. putida P13 and Azotobacter sp. SP5 lost their P-solubilization ability while Pseudomonas sp. C16-2O and P. fluorescens Tabriz were the best solubilizers and they solubilized 185.3 and 182.7mgL−1 of insoluble P. P solubility in presence of TCP was 2.55 times more than RP source.

Assessment of two carrier materials for phosphate solubilizing biofertilizers and their effect on growth of wheat (Triticum aestivum L.)

Biofertilizers are usually carrier-based inoculants containing beneficial microorganisms. Incorporation of microorganisms in carrier material enables easy-handling, long-term storage and high effectiveness of biofertilizers. Objective of the present study was to assess enriched biogas sludge and soil as biofertilizer carriers on growth and yield of wheat. Six phosphate solubilizing strains were used in this study. Three phosphate solubilizing strains, 77-NS2 (Bacillus endophyticus), 77-CS-S1 (Bacillus sphaericus) and 77-NS5 (Enterobacter aerogenes) were isolated from the rhizosphere of sugarcane, two strains, PSB5 (Bacillus safensis) and PSB12 (Bacillus megaterium) from the rhizosphere of wheat and one halophilic phosphate solubilizing strain AT2RP3 (Virgibacillus sp.) from the rhizosphere of Atriplex amnicola, were used as bioinoculants. Phosphate solubilization ability of these strains was checked in vitro in Pikovskaya medium, containing rock phosphate (RP) as insoluble P source, individually supplemented with three different carbon sources, i.e., glucose, sucrose and maltose. Maximum phosphate solubilization; 305.6μg/ml, 217.2μg/ml and 148.1μg/ml was observed in Bacillus strain PSB12 in Pikovskaya medium containing sucrose, maltose and glucose respectively. A field experiment and pot experiments in climate control room were conducted to study the effects of biogas sludge and enriched soil based phosphorous biofertilizers on growth of wheat. Bacillus strain PSB12 significantly increased root and shoot dry weights and lengths using biogas sludge as carrier material in climate control room experiments. While in field conditions, significant increase in root and shoot dry weights, lengths and seed weights was seen by PSB12 and PSB5 (Bacillus) and Enterobacter strain 77-NS5 using biogas sludge as carrier. PSB12 also significantly increased both root and shoot dry weights and lengths in field conditions when used as enriched soil based inoculum. These results indicated that bacterial isolates having plant beneficial traits such as P solubilization are more promising candidates as biofertilizer when used with carrier materials.

Trichoderma virens Mediated Rock Phosphate Solubilization: A Potential Replacement For Triple Super Phosphate in Rice Cultivation

Annually, Sri Lanka spends 20 billion Rupees to import Triple super Phosphate (TSP) mainly for the rice cultivation. It has been recorded that, significantly high arsenic content is present in imported TSP compared to Eppawala Rock phosphate (ERP). Further, the current understanding is that arsenic is among the major etiological agents of Chronic Kidney Disease. Hence, a progressive reduction in the use of TSP in rice cultivation may help in reducing health and environmental problems associated with it. Yet the major constraint in the use of ERP in rice cultivation is its low solubility. As microorganisms are efficient solubilizers of Rock phosphate, attempts were made to employ a local isolate of Trichodrema virens, which has a proven track record for ERP solubilization, to increase the solubility of ERP with the aim of developing an environmentally friendly liquid P fertilizer. A pot experiment was conducted at Rice Research and Development Institute at Batalagoda. An amended Pikovskaya (PVK) medium with ERP was inoculated with T. virens containing 1X 106 spores/ml and incubated at 100 rpm oscillation until maximum solubilized P content was obtained. The filtered and autoclaved culture filtrate was applied to the rice variety Bg 250 one week before transplanting. Fertilizer application included: Control without any fertilizer (C1), control with recommended level of MOP, urea and no P (C2), Control with PVK medium without P source (C3), TSP at recommended level (P1), TSP at half recommended level together with developed fertilizer added to replace half recommended level of TSP quantitatively (P2), TSP at half recommended level (P3), developed fertilizer applied at recommended level of TSP (P4). Additionally, the recommended level of MOP and Urea was applied to every treatment except for C1. Completely randomized design was employed with 12 replicates and each pot containing 4 rice plants. Plant growth parameters and plant and soil P contents were quantitatively determined by destructive sampling of 04 replicates from each treatment at tillering stage and at 50% flowering stage while yield parameters with plant and soil P were measured at harvesting stage. The results obtained were analyzed using T test and one way ANOVA. During fertilizer development, maximum P content (42.55 mg P/l) was obtained at 72 hour post incubation. All the studied parameters differed significantly among treatments (P = 0.000). Superior growth and yield performance were shown by P2 where the performance was not significantly different from that of P1 for all the tested parameters. Even though treatment P4 was not superior to treatment P1, it was significantly superior to P3. Hence, the data suggests the possibility of reducing the recommended level of TSP into half by using the developed liquid fertilizer to minimize TSP usage. Keywords: Trichodrema virens, Phosphorus, Eppawala rock phosphate, Rice, Growth parameters, Yield parameters

Documentation of five potassium- and phosphorus-solubilizing bacteria for their K and P-solubilization ability from various minerals

Abstract The ability of a few soil bacteria to transform unavailable forms of phosphorus (P) and potassium (K) to an available form is an important feature in plant growth-promoting bacteria for increasing crop yields of high- P and K-demand crops. In this research, screening and characterization of thirty-five K-solubilizing bacterial (KSB) and P-solubilizing bacteria (PSB) isolate which were evaluated for their ability to solubilize K and P from the waste muscovite (WM), waste biotite (WB), tri-calcium phosphate (TCP) and rock phosphate (RP) by analyzing the soluble P and K content after 7, 14, 21 days after incubation (DAI) at 28±2 °C on MABs (Modified Aleksandrov Broths) and Pikovskaya's medium. The soluble P and K contents in all isolates were significantly (p

Characterization and Identification of Phosphate Solubilizing Bacteria Isolate GPC3.7 from Limestone Mining Region

Phosphate (P) are one of major macronutrients needed by plants. P in the soil are present in the organic and inorganic form. The amounts of P in marginal soil can be increased with plant growth promoting rhizobacteria (PGPR). The aim of this study was to characterize and identify P solubilizing bacteria (PSB) isolate GPC3.7 that characteristically could fix N from the soil around limestone mining area. There were 44 PSB isolates found from 15 soil samples around limestone mining area, Blindis mountain, Cirebon. The solubility index of all strain were measured about 0.125 to 2.375 on Pikovskaya media. There were 22 PSB isolates were grown on N-free bromothymol blue (NfB) medium and 19 isolates were grown on Congo Red Agar (CRA) medium. Only 10 isolates were indicated as symbiotic living microorganisms whereas 12 others were categorized as N-free fixing bacteria. Isolate GPC3.7 was chosen to be further observed, based on its P solubility index, N-fixing ability and growth stability. Phosphate quantitative estimation assay of isolate GPC3.7 was unmeasured. The P soluble concentration of GPC3.7 might be lower than 1 mg/L. The colony of GPC3.7 morphologically had round shape, entire margin, raised elevation and white color. Isolate GPC3.7 was Gram negative bacteria with coccus cell shape. Based on 16S rRNA gene, GPC3.7 was closely relative to Acinetobacter baumannii.

Heavy Metal Removal by Phosphate Solubilizing Acinetobacter calcoaceticus Isolated from Rhizosphere

Worldwide industrial activities produce large amount of metal wastes. Metals remediation by microbial activities associated with phosphorus metabolism is a promising method. The goals of this study were the removal of some heavy metals by isolated phosphate solubilizing rhizobacterium (PSR) and survey the effect of total secreted materials including extracellular phosphatase on this phenomenon. PSR strain was isolated by Pikovskaya (PVK) medium and identified by 16S rDNA sequencing. Its phosphatase enzyme was assayed by colorimetric method. Metal resistance of the isolate was measured by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The metal removal was detected by atomic absorption spectroscopy. The culture supernatant was analyzed for metal removal by secreted phosphatase enzyme with or without tri-calcium phosphate (TCP), as its substrate. The isolated rhizobacterium was identified as Acinetobacter calcoaceticus that produced acid phosphatase enzyme. The MICs50 were obtained 2.5 mM Pb(II), 2 mM Ni(II), 0.2 mM Cr(II) and E‚1 mM Cd(II); and the MBCs were >100 mM Ni(II), 40 mM Cd(II), 20 mM Pb(II), and 1 mM (Cr(II). The removal of metals by the cells were obtained 29.45% Cr(II), 25.74% Pb(II), 18.85% Cd(II) and 11.43% Ni(II). It was not seen any nickel removal by microbial secreted products in PVK medium without TCP, whereas removal was obtained in PVK complimented by TCP 28.3%; lead removal was almost the same in both media (99%) and was not related to TCP.

Phosphate solubilizing bacteria from the acidic soils of Eastern Himalayan region and their antagonistic effect on fungal pathogens

This study tries to identify the native population of phosphate solubilizing bacteria (PSB) in the rhizospheres of maize, rice, ginger and large cardamom grown in different regions of Sikkim (India). Out of 104 rhizospheric samples collected from three agroclimatic zones of the state, 42 number of PSBs were isolated. However, only 26 best performing PSB based upon their solubilization in solid media are reported in this paper. The highest number of PSB with greatest variants were found in the rhizosphere of rice.The population density of PSB varies between 2–36×106cfug−1. Based upon the morphological and 16S rRNA sequencing, the isolates were clustered under the genera Bacillus, Pseudomonas, Micrococcus, Staphylococcus, Microbacterium and Delftia. Phosphate solubilization efficiency of these isolates varied between 46 to 160% in solid medium and in the liquid Pikovskaya's medium phosphate solubilization capacity varied between 30.2 to 203.7mgL−1. Though all of the isolates were able to solubilize aluminum and iron phosphate significantly however, they solubilized Ca3(PO4)2 to a greater extent than the other two with AlPO4 exhibiting comparatively poor solubilization among the three phosphate sources. Further, the in vitro antagonistic effect of the PSB isolates were studied with seven locally available fungal pathogens and it revealed that the Bacillus amyloliquefaciens PSB isolates showed higher antifungal activity against soil and root borne pathogens (Rhizoctonia sp., Pythium sp., Fusarium sp.) than the leaf pathogens.

Isolation and identification by 16S rRNA sequence analysis of plant growth-promoting azospirilla from the rhizosphere of wheat.

The main objective of the present study was to isolate phytohormone-producing, phosphate-solubilizing strains of Azospirillum from wheat to be used as inoculants for plant growth promotion. Five Azospirillum strains were isolated from the rhizosphere of field-grown wheat (Triticum aestivum L.), and it was confirmed by BOX-polymerase chain reaction (PCR) that the isolates were different and not re-isolates of the same strain. Sequence analysis of the PCR-amplified 16S rRNA gene indicated that four isolates showed maximum similarity to Azospirillum brasilense and one isolate showed maximum similarity to Azospirillum zeae. This is the first report indicating the presence of an A. zeae like isolate in the wheat rhizosphere in Pakistan. The bacterial isolates were characterized for their plant growth-promoting traits, phosphate solubilization, and indole-3-acetic acid (IAA) production. None of the isolates showed phosphate solubilization activity in the commonly used Pikovskaya medium. However, all strains (except AzoK4) exhibited ability to solubilize tricalcium phosphate (TCP) in modified Pikovskaya medium in which sucrose was replaced by Na-malate, as well as in TCP-supplemented Luria-Bertani (LB) medium. Organic acids, such as acetic, citric, lactic, malic, and succinic acids, were detected in culture supernatants of the tested Azospirillum strains. All strains exhibited ability to produce IAA in the growth medium, except Azospirillum sp. AzoK1. Among the strains tested, the maximum IAA production (30.49 ± 1.04 mg L−1) and phosphate solubilization (105.50 ± 4.93 mg L−1) were shown by a pure culture of Azospirillum sp. AzoK2. In pot experiments, single-strain inocula of Azospirillum sp. AzoK1 and AzoK2 improved wheat plant growth.

Phosphate Solubilization Potential of Rhizosphere Fungi Isolated from Plants in Jimma Zone, Southwest Ethiopia.

Phosphorus (P) is one of the major bioelements limiting agricultural production. Phosphate solubilizing fungi play a noteworthy role in increasing the bioavailability of soil phosphates for plants. The present study was aimed at isolating and characterizing phosphate solubilizing fungi from different rhizospheres using both solid and liquid Pikovskaya (PVK) medium. A total of 359 fungal isolates were obtained from 150 rhizosphere soil samples of haricot bean, faba bean, cabbage, tomato, and sugarcane. Among the isolates, 167 (46.52%) solubilized inorganic phosphate. The isolated phosphate solubilizing fungi belonged to genera of Aspergillus (55.69%), Penicillium spp. (23.35%), and Fusarium (9.58%). Solubilization index (SI) ranged from 1.10 to 3.05. Isolates designated as JUHbF95 (Aspergillus sp.) and JUFbF59 (Penicillium sp.) solubilized maximum amount of P 728.77 μg·mL−1 and 514.44 μg mL−1, respectively, from TCP (tricalcium phosphate) after 15 days of incubation. The highest (363 μg mL−1) soluble-P was released from RP with the inoculation of JUHbF95 in the PVK broth after 10 days of incubation. The present study indicated the presence of diverse plant associated P-solubilizing fungi that may serve as potential biofertilizers.

Isolation of Phosphorus-Solubilizing Fungus from Soil to Supplement Biofertilizer

A number of bacterial and fungal isolates from soil were screened for phosphorus solubilization. One fungal strain was found to be efficient phosphorus solubilizer in Pikovskaya medium. The selected strain was identified as Aspergillus niger based on morphological and microscopic studies. Some important cultural conditions were optimized, and optimal conditions for temperature, glucose, ammonium sulfate and pH were found \({30^{\circ}{\rm C}}\), 20, 2 and 5 g/L, respectively, in 48 h of incubation. The fungal strain produces organic acids as well as phosphatases and phytases that make the medium clear within 48 h by solubilizing the added tricalcium phosphate. The soluble phosphorus concentration of medium decreased after 48 h of incubation, possibly due to the consumption of phosphorus by the fungal mycelium itself.

Biodegradation of chlorpyrifos and its hydrolysis product 3,5,6-trichloro-2-pyridinol using a novel bacterium Ochrobactrum sp. JAS2: A proposal of its metabolic pathway

Biodegradation of chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol (TCP) were studied with a novel bacterial strain JAS2 isolated from paddy rhizosphere soil. The molecular characterization based on 16S rRNA gene sequence homology confirmed its identity as Ochrobactrum sp. JAS2. The JAS2 strain degraded 300mgl−1 of chlorpyrifos within 12h of incubation in the aqueous medium and it produced the TCP metabolite. However, after 72h of incubation TCP was also completely degraded by the JAS2 strain. A tentative degradation pathway of chlorpyrifos by Ochrobactrum sp. JAS2 has been proposed on basis of GC–MS analysis. The complete degradation of chlorpyrifos occurred within 24h in the soil spiked with and without addition of nutrients inoculated with Ochrobactrum sp. JAS2. TCP was obtained in both the studies which was degraded completely by 96h in the soil spiked with nutrients and whereas 120h in absence of nutrients in the soil. The mpd gene which is responsible for organophosphorus hydrolase production was identified. The isolates Ochrobactrum sp. JAS2 also exhibited a time dependent increase in the amount of tricalcium phosphate solubilization in Pikovskaya's medium. Further screening of the strain JAS2 for auxiliary plant growth promoting activities revealed its remarkable capability of producing the indole acetic acid (IAA), hydrogen cyanide (HCN) and ammonia.

Solubilization of inorganic phosphate by Pseudomonas strains isolated from rice rhizosphere

The use of phosphate solubilizing bacteria to mobilize large reserves of insoluble P in soils instead of phosphate fertilizers is an ecologically safe and economically reasonable alternative to assure a sustainable agriculture. In this work, the mineral phosphate solubilization activity was evaluated for 4 Pseudomonas strains isolated from rice rhizosphere. For qualitative tests, different media were used; NBRIP, YED and Pikovskaya (PVK) amended with 0.5% Ca3(PO4)2 and modified PVK medium containing CaHPO4, Ca5HO13P3, FePO4 and AlPO4 as P source. All bacteria were able to dissolve calcium phosphates, while none was surrounded by transparent halos when FePO4 and AlPO4 were the P source. Quantitative test was assessed in PVK substituting glucose by sucrose and galactose. The highest levels of soluble P were recorded in the presence of glucose, while it didn’t exceed 43.64 μg / ml and 19.19 µg / ml in the presence of galactose and sucrose, respectively. Therefore, glucose has been chosen as a carbon source to assay the effect of carbon concentration on P solubilization ability. The level of dissolved P was enhanced with increasing amount of glucose (1%, 2% and 3% (w/v)). In all cases, the P biosolubilisation was accompanied by a significant pH decrease of the liquid media. A significant inverse correlation was found between P concentrations and pH reduction. Thus, acidification of the media seems to be the main mechanism for calcium phosphates solubilization in this study, and these test strains could serve as efficient biofertilizer candidates for improving crop production in low P soils.

Uranium(VI) bioprecipitation mediated by a phosphate solubilizing Acinetobacter sp. YU-SS-SB-29 isolated from a high natural background radiation site

Bioprecipitation of uranium (U) into uranyl phosphate (U-P) mediated by soluble ortho-phosphate is an attractive proposition for U bioremediation. As an alternative to the microbial phosphatase, we have investigated the dissolution of phosphate by the organic acids produced by bacteria to aid in U precipitation. The bacterium Acinetobacter sp. YU-SS-SB-29, isolated from monazite sand of natural background radiation site solubilized 952.0 ± 46.7 mg L−1 phosphate from tri-calcium phosphate (TCP) in the Pikovskaya's medium and showed tolerance to 120 ppm U(VI). U(VI) bioprecipitation was investigated by adding different concentrations of U(VI) to a cell-free culture supernatant containing ortho-phosphate released from TCP by the bacterium. A yellow precipitate was immediately formed following which there was a reduction in U(VI) concentration. A strong positive correlation (R2 = 0.98) was observed between % decrease in phosphate and U(VI) concentration (up to 750 ppm U) added. FTIR and EDX spectra of the yellow precipitate demonstrated the involvement of phosphate groups in U(VI) binding. Furthermore, the XRD pattern of the precipitate agrees well with that of chernikovite, a uranyl phosphate mineral. The results from this study demonstrate the potential of the U tolerant, phosphate solubilizing bacterium Acinetobacter sp. YU-SS-SB-29 for non-reductive in situ bioprecipitation of uranium.

Isolation and characterization of phosphate-solubilizing bacteria from betel nut (Areca catechu) and their effects on plant growth and phosphorus mobilization in tropical soils

Phosphate-solubilizing bacteria (PSB) were isolated and characterized from the rhizosphere and bulk soils of Areca catechu plants. A long history of phosphate fertilizer use has elicited a direct effect on the incidence of soil PSB. Their abundance and ability to solubilize insoluble phosphate were significantly greater (P < 0.0001) in soils with low available phosphorus (P) content than in other soil types. Three efficient PSB strains, namely, ASL12, ASG34, and ADH302, were identified as Acinetobacter pittii, Escherichia coli, and Enterobacter cloacae by characterizing 16S rRNA sequences and biochemical characteristics; they produced gluconic acid at concentrations of 7862.4, 4306.5, and 2663.8 mg L−1, respectively. The highest amount of solubilized P was determined in Pikovskaya (PVK) medium for the bacterial strain ASL12. The secretion of gluconic acid was related to the available P of rhizosphere soils and P solubilization. Under shaded conditions, the application of these three strains significantly improved plant height, shoot and root dry weight, and nutrient uptake of A. catechu seedlings. A further increase in P solubilization was observed by co-inoculating the three strains and also applying tricalcium phosphate (TCP) or aluminum phosphate (AP). A significant (P < 0.05) correlation was also observed between P-solubilization activity and A. catechu plant growth in pot experiments. Thus, the three strains can be potentially applied as inoculants in tropical and aluminum-rich soils.

Efficiency of plant growth‐promoting P‐solubilizing Bacillus circulans CB7 for enhancement of tomato growth under net house conditions

P-solubilizing bacterial isolate CB7 isolated from apple rhizosphere soil of Himachal Pradesh, India was identified as Bacillus circulans on the basis of phenotypic characteristics, biochemical tests, fatty acid methyl esters analysis, and 16S rRNA gene sequence. The isolate exhibited plant growth-promoting traits of P-solubilization, auxin, 1-aminocyclopropane-1-carboxylate deaminase activity, siderophore, nitrogenase activity, and antagonistic activity against Dematophora necatrix. In vitro studies revealed that P-solubilization and other plant growth-promoting traits were dependent on the presence of glucose in PVK medium and removal of yeast extract had no significant effect on plant growth-promoting traits. Plant growth-promoting traits of isolate CB7 were repressed in the presence of KH2 PO4 . P-solubilization activity was associated with the release of organic acids and a drop in the pH of the Pikovskaya's medium. HPLC analysis detected gluconic and citric acid as major organic acids in the course of P-solubilization. Remarkable increase was observed in seed germination (22.32%), shoot length (15.91%), root length (25.10%), shoot dry weight (52.92%) and root dry weight (31.4%), nitrogen (18.75%), potassium (57.69%), and phosphorus (22.22%) content of shoot biomass over control. These results demonstrate that isolate CB7 has the promising PGPR attributes to be developed as a biofertilizer to enhance soil fertility and promote plant growth.

10.5937/ratpov51-6222 = Solubilization of inorganic phosphate by endophytic Pseudomonas sp. from French bean nodules

Phosphorus (P) is one of the major essential macronutrient for plant growth. Phosphate solubilizing bacteria (PCB) is a group of heterotrophic bacteria capable of solubilizing organic and inorganic phosphorus from insoluble compounds, releasing phosphate available for plant uptake. In this study endophytic bacteria were isolated form nodules of French bean grown in different intercropping systems. Only 14 out of 158 endophytic isolates were able to solubilize tricalcium phosphate (TCP). None of them were observed to solubilize FePO4 and AlPO4. Eight isolates formed solubilization zones larger than 3 mm and were used for further test. The TCP solubilization was measured in liquid Pikovskaya medium and ranged from 14-182 μgml-1 of soluble phosphorus. TCP solubilization was correlated with acidity and pH decreasing from 7.4 to 5.57 and 4.91 for the lowest and the highest solubilizer, respectively, were observed. The most efficient isolate MP18 was selected and identified as Pseudomonas sp. according to 16S rRNA gene analysis.